A VCSEL is a laser device formed from an optically active semiconductor region that is sandwiched between a pair of highly reflective mirror stacks, which may be formed from layers of metallic material, dielectric material, or epitaxially-grown semiconductor material. Recently, efforts have been made to extend the operating wavelengths of VCSEL devices to the shorter wavelength range of 200 nm to 600 nm (i.e., the violet to red region of the visible light spectrum). Many nitride semiconductor materials (e.g., GaN based materials, such as GaN, AlGaN, and AlInGaN) have bandgap energies that correspond to this wavelength range. For this reason, significant efforts have been made to fabricate nitride semiconductor light emitting devices that produce light in this wavelength range.
One of the challenges associated with designing high-performance nitride semiconductor VCSELs relates to the high-resistance p-type intra-cavity contacts that typically are formed with nitride semiconductor material. These contacts increase the voltage drop and increase the heat generated within the VCSELs. Another challenge relates to the limited number of quantum wells that can be incorporated in vertical current injection type of VCSEL designs due to non-uniform pumping effects. This limits the optical gain performance that can be achieved.